<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input type="text" id="i1">
<input type="text" id="i2">
<input type="button" value="加" onclick="f(1)">
<input type="button" value="减" onclick="f(2)">
<input type="button" value="乘" onclick="f(3)">
<input type="button" value="除" onclick="f(4)">
<div>结果:<b></b></div>
<script>
    function f(x) {
        let i1 = document.querySelector("#i1")
        let i2 = document.querySelector("#i2")
        let d = document.querySelector("b")
        if (isNaN(i1.value)||isNaN(i2.value)){
            d.innerText ="输入错误"
            return
        }

    switch (x) {
        case 1:
            d.innerText = i1.value*1+i2.value*1;
            break;
        case 2:
            d.innerText = i1.value-i2.value;
            break;
        case 3:
            d.innerText = i1.value*i2.value;
            break;
        case 4:
            d.innerText = i1.value/i2.value;
            break;

    }
    function f1() {
        let i1 = document.querySelector("#i1")
        let i2 = document.querySelector("#i2")
        let d = document.querySelector("b")
        d.innerText = i1.value*1+i2.value*1;
    }
    function f2() {
        let i1 = document.querySelector("#i1")
        let i2 = document.querySelector("#i2")
        let d = document.querySelector("b")
        d.innerText = i1.value-i2.value;
    }
    function f3() {
        let i1 = document.querySelector("#i1")
        let i2 = document.querySelector("#i2")
        let d = document.querySelector("b")
        d.innerText = i1.value*i2.value;
    }
    function f4() {
        let i1 = document.querySelector("#i1")
        let i2 = document.querySelector("#i2")
        let d = document.querySelector("b")
        d.innerText = i1.value/i2.value;
    }
</script>
</body>
</html>